2 missed periods, some spotting, larger breasts, highly emotional, 20 yrs old, took 1 pregnancy test a month ago that was negative, what's the cause?

2 missed periods: I suggest that you check another pregnancy test and if it is negative you need to see your physician especially if this is new for you. There are a number of reasons other than pregnancy for missed periods -- one of them is polycystic ovaries. Other causes include malnutrition, excessive exercise or certain birthcontrol pills.

Need to examine: If you had sex since your last period, do a home pregnancy test. It may help to get a blood test for HCG level. For causes of irregular periods, visit this site for info: http://www.nichd.nih.gov/health/topics/menstruation/conditioninfo/Pages/causes.aspx